Make sure you are using the right size pump kit — it should be comfortable and your nipples should slide without rubbing against the parts. Pumping very often (every hour or so during the day when you are awake) for a few days can help increase your supply. If this doesn't work, try a different type or brand of pump. There are also medications that can be helpful. A breastfeeding medicine doctor (MD, IBCLC) can assess your situation and prescribe medicine to help.